1. Technical Field
The present invention relates generally to data processing networks, and more particularly to a data processing network in which a multiplicity of host processors are connected to shared resources.
2. Related Art
In many data processing networks, a large number of host processors share resources such as a database or storage subsystem. Typically, each host has a high probability of obtaining immediate access, but immediate access is not guaranteed. The cost of guaranteeing immediate access is usually considered to be much greater than the benefit to the user.
The probability of obtaining immediate access can be increased by using various techniques. A direct but rather costly solution is to provide additional network paths and additional storage resources, such as additional paths to duplicate storage servers for read-only storage volumes. Other techniques, such as dynamic routing and load balancing, attempt to use existing network and storage resources more effectively.
Dynamic routing directs each data access requests along a path that is selected in accordance with the resources that are currently available in order to avoid overload of resources in the network. Load balancing assigns alternative resources to the hosts in order to avoid overload of any one of the alternative resources by receipt of simultaneous access requests from a large number of the hosts. For dynamic routing and load balancing to be particularly effective, however, additional resources are required in order to gather intelligence about the current or expected state of the network, and to control or restrict the path of the data access requests in a fashion that is beneficial. These additional resources tend to introduce cost and complexity into the data network and often reduce performance during usual operating conditions.
In accordance with one aspect of the invention, there is provided a method of routing resource requests through a switch in a data processing network. The method includes storing, in a memory, routing information defining respective outputs of the switch to which resource requests received at inputs of the switch should be routed. In response to resource requests being received at the inputs of the switch, each resource request received at each input of the switch is routed to an output of the switch by accessing the routing information in the memory to select a respective output of the switch to which the resource request should be routed, and routing the resource request to the selected output of the switch to which the resource request should be routed. The method further includes changing the routing information stored in the memory based on loading characteristics of the resource requests received at the switch inputs.
In accordance with another aspect of the invention, there is provided a method of routing storage access requests from host processors through a switch to a data storage subsystem. The switch has inputs coupled to the hosts to receive the storage access requests from the hosts, and the switch has outputs coupled to the data storage subsystem to transmit the storage access requests to the data storage subsystem. The method includes storing, in a memory, routing information defining respective outputs of the switch to which storage access requests received at inputs of the switch should be routed. In response to storage access requests being received at the inputs of the switch, each storage access request received at each input of the switch is routed to an output of the switch by accessing the routing information in the memory to select a respective output of the switch to which the storage access request should be routed, and routing the storage access request to the selected output of the switch to which the storage access request should be routed. The method further includes changing the routing information stored in the memory based on loading characteristics of the storage access requests received at the switch inputs.
In accordance with yet another aspect of the invention, there is provided a switch for routing resource requests in a data network. The switch includes plurality of inputs, a plurality of outputs, and a switch control computer programmed for routing the resource requests from the inputs to the outputs. The switch control computer includes memory storing routing information, and the routing information defines respective outputs of the switch to which resource requests received at the inputs of the switch should be routed. The switch control computer is programmed to respond to receipt of the resource requests at the inputs of the switch by routing each resource request received at each input of the switch to an output of the switch by accessing the routing information in the memory to select a respective output of the switch to which the resource request should be routed, and to route the resource request to the selected output of the switch to which the resource request should be routed. The switch control computer is further programmed to change the routing information stored in the memory based on loading characteristics of the resource requests received at the switch inputs.
In accordance with still another aspect of the invention, there is provided a program storage device containing a program for a switch for routing resource requests in a data network according to routing information stored in a memory. The routing information defines respective outputs of the switch to which resource requests received at the inputs of the switch should be routed. The program is executable by the switch for responding to receipt of the resource requests at the inputs of the switch by routing each resource request received at each input of the switch to an output of the switch by accessing the routing information in the memory to select a respective output of the switch to which the resource request should be routed, and to route the resource request to the selected output of the switch to which the resource request should be routed. The program is further executable by the switch to change the routing information stored in the memory based on loading characteristics of the resource requests received at the switch inputs.
In accordance with a final aspect of the invention, there is provided a storage network including a cached storage subsystem and a switch. The cached storage subsystem includes a plurality of storage devices, a cache memory linked to the storage devices for filling the cache with data from the storage devices, and a plurality of port adapters providing storage ports for access to the cache memory. The switch has a plurality of inputs for receiving data access requests from a plurality of hosts, and a plurality of outputs linked to the storage ports for selectively routing data access requests from the inputs of the switch to the storage ports. The storage network further includes a memory containing routing information. The routing information defines respective outputs of the switch to which storage access requests received at the inputs of the switch should be routed. The switch is programmed to respond to receipt of the storage access requests at the inputs of the switch by routing each storage access request received at each input of the switch to a selected output of the switch by accessing the routing information in the memory to select an output of the switch to which the each storage access request should be routed, and to route the storage access request to the selected output of the switch to which the storage access request should be routed. The storage network further includes a processor programmed to change the routing information in the memory based on loading characteristics of the storage access requests.